Congo red

Author: Nat Pernick, M.D.

Revised: 10 May 2018, last major update October 2013

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Congo red[title] stain
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Cite this page: Pernick, N. Congo red. website. Accessed February 18th, 2019.
Definition / general
  • Also called amyloid stain
  • Must examine stained tissue with standard and polarized light
  • Amyloid under polarized light has apple green birefringence, based on the molecule being in an antiparallel beta-pleated sheet.
  • Note: non-amyloid related green birefringence can occur due to excess dye retained by the tissue
Microscopic (histologic) images

Images hosted on other servers:

Medullary carcinoma
of thyroid gland
staining lower right

Amyloid in adrenal gland

Primary localized
laryngeal amyloidosis
(polarized light-fig F)

Fig 1: coarse calcifications of right breast
Fig 2: H&E
Fig 3: congo red staining
Fig 4: congo red under polarized light